You could try running the android version if you have it.
Much lower system specs, so should run smooth as butter.
Never done it myself, but I hear it's easy enough to run it on linux.
You don't need the paid edition just for occasional scans.
If you click buy while logged in, you should get a screen saying "You already own minecraft" and it should give you a download page.
You used to be able to get to that page by going to minecraft.net/download, but they've crippled the site and removed it.
Essentially, you just need to download the launcher and log in with your email and password.
There is no easy way I know of, because as far as I'm aware the game is hardcoded to use that folder for some reason.
You can create a symlink to the location you want it, but it's complicated.
I don't really have all these issues people have :\
I've dedicated Minecraft 10GB of ram and it runs at a pretty solid 85FPS on 18chunk render, max settings and I get very few stutters.
I don't really play on servers anymore, so maybe its all server related. Lighting is a tiny bit off, but not enough for me to care much.
You absolutely do not want to do that.
Minecraft is made in Java, and it has a garbage collector thing.
Essentially, if you have too much RAM allocated, it makes a massive file, that then causes a massive lag spike when it's deleted.
Is the left most screenshot even yours?
It's got a different GPU and CPU to the right one.
The right hand one is actually decently powerful, and the CPU and GPU is more than sufficient.
You will be able to open the old world, in the latest update, but the changes will only effect chunks you haven't loaded.
So basically, everywhere you have explored, will still have all the old oceans, etc.
There is an option to backup the world in the world selection screen now, along with an option to convert.
You'll want to use both of these.